244 HUMAN ANATOMY. 



maxilla, ending, therefore, opposite the space between the lateral incisor and the 

 canine. In single harelip, which is often associated with cleft palate, and due to 

 faulty union of the fronto-nasal and maxillary processes (page 60), the gap is found 

 at the same point, never in the middle line. Sometimes the premaxillary bone, 

 which carries the two upper central incisors, is left attached to the nose. This con- 

 dition is usually associated with double harelip. Cleft palate may involve only the 

 soft palate and not the hard, but the reverse is almost never true. 



Occasionally the identity of the premaxilla is" established pathologically. 

 Instances of exfoliation of this bone carrying the two incisor teeth have been 

 recorded, not only in children but^even in adults. 



ExcisioJi of the superior viaxilla involves (the bone having been exposed by a 

 suitable incision through the soft parts) the disjunction of (a) its connection with 

 the malar bone ; {b) its nasal process from the nasal, lachrymal, and frontal bon^ ; 

 (<:) its orbital plate from the ethmoid, malar, lachrymal, and palate bones ; (^) its 

 posterior connection with the pterygoid processes and palate bone ; and (<?) its 

 articulation with its fellow through the palatal plates and its connection with the soft 

 palate. 



These indications are met, as a rule, by sawing through the malar bone just 

 beyond its articulation with the maxilla (so that advantage may be taken of the 

 proximity of the spheno-maxillary fissure), dividing the nasal process a little below 

 the junction with the nasal bones, sawing through the hard palate (from the nose 

 downward) at or beyond the median line, dividing the orbital plate with a fine 

 chisel (or leaving it to be brought away at the last step), and, finally, wrenching 

 the bone away from its attachment to the pterygoid processes (and the orbit) by 

 means of a pair of lion-forceps. The hinder wall, in contact with the palate bone, 

 is very thin, and may give vv'ay and remain behind at this stage. This is most likely 

 to happen when it is most undesirable, — i.e.^ when the operation is performed for 

 malignant disease. 



The inferior maxilla, the only bone of the skull which is movable upon the 

 others, is especially dense, so that it may be strong enough to withstand the very 

 considerable force which its muscles exert upon it in mastication. It is, therefore, 

 not easily divided in operations. The alveolar processes are thicker and stronger 

 than those of the upper jaw, and more force is, therefore, usually required to extract 

 a tooth ; hence damage to the bone through rough or unskilful effort at extraction 

 is more frequent in the lower than in the upper jaw. The last molar, or wisdom 

 tooth, is often a cause of trouble, owing to the limited space it occupies near the 

 angle between the ramus and the body of the jaw. The smaller that angle the 

 greater the difficulty in cutting this tooth, which may be compelled to carry before 

 it a portion of the gum closely applied to the base of the coronoid process, causing 

 inflammation or ulceration, or, through irritation of the sensory branches of the fifth 

 nerve, may even produce trismus, since the motor supply of the muscles of mastica- 

 tion is derived from the same nerve-trunk. It is thus much oftener the source of 

 trouble in the white races than in negroes, in whom the angle between the ascending 

 and horizontal portions of the bone is more obtuse. 



Congenital deformities of the lower jaw are very rare. When they do occur, 

 as in a case reported by Humphry, they show that the jaw consists essentially of two 

 portions, the alveolus and the remainder of the jaw. In that case the jaw in adult 

 life preserved the proportions of infancy so far as the body was concerned, but the 

 teeth and alveolus had attained normal dimensions. The division, as Allen has 

 emphasized, is an important one to remember for the following reasons : the alveolus 

 is developed with the teeth ; it is an outgrowth from the jaw for a specific temporary 

 purpose. John Hunter declared that the "alveolar processes of both jaws should 

 rather be considered as belonging to the teeth than as parts of the jaws." Hence 

 all diseases of the alveolus are to be considered as dental in their significance. 

 Epulis, or fibroma of the gums, is essentially an alveolar disease. A tooth in any 

 portion of the jaw other than the alveolus is a foreign body. If it is lodged beneath 

 the alveolus, it may give rise to chronic abscess, or may, through long-continued 

 irritation, cause one of the various forms of odontomata. Cystic disease about the 

 angle of the jaw is often excited by a misplaced third molar. 



